Communication devices such as wireless communication devices, that simply may be named wireless devices, may also be known as e.g. user equipments (UEs), mobile terminals, wireless terminals and/or mobile stations. A wireless device is enabled to communicate wirelessly in a wireless communication network, wireless communication system, or radio communication system, e.g. a telecommunication network, sometimes also referred to as a cellular radio system, cellular network or cellular communication system. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communication network. The wireless device may further be referred to as a mobile telephone, cellular telephone, laptop, Personal Digital Assistant (PDA), tablet computer, just to mention some further examples. Wireless devices may be so called Machine to Machine (M2M) devices or Machine Type of Communication (MTC) devices, i.e. devices that are not associated with a conventional user.
The wireless device may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
The wireless communication network may cover a geographical area which is divided into cell areas, wherein each cell area is served by at least one base station, or Base Station (BS), e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is typically identified by one or more cell identities. The base station at a base station site may provide radio coverage for one or more cells. A cell is thus typically associated with a geographical area where radio coverage for that cell is provided by the base station at the base station site. Cells may overlap so that several cells cover the same geographical area. By the base station providing or serving a cell is typically meant that the base station provides radio coverage such that one or more wireless devices located in the geographical area where the radio coverage is provided may be served by the base station in said cell. When a wireless device is said to be served in or by a cell this implies that the wireless device is served by the base station providing radio coverage for the cell. One base station may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the wireless device within range of the base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunication System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communication (originally: Groupe Spécial Mobile), which may be referred to as 2nd generation or 2G.
UMTS is a third generation mobile communication system, which may be referred to as 3rd generation or 3G, and which evolved from the GSM, and provides improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for wireless devices. High Speed Packet Access (HSPA) is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), defined by 3GPP, that extends and improves the performance of existing 3rd generation mobile telecommunication networks utilizing the WCDMA. Such networks may be named WCDMA/HSPA.
The expression downlink (DL) is used for the transmission path from the base station to the wireless device. The expression uplink (UL) is used for the transmission path in the opposite direction i.e. from the wireless device to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or eNBs, may be directly connected to other base stations and may be directly connected to one or more core networks. LTE may be referred to as 4th generation or 4G.
The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies, for example into evolved UTRAN (E-UTRAN) used in LTE.
Work is ongoing with developing a next generation wide area networks, which may be referred to as NeXt generation (NX), New Radio (NR), or fifth generation (5G). A design principle under consideration for 5G wireless communication networks is to base it on an ultra-lean design. This implies that “always on signals”, such as reference signals in LTE, shall be avoided in the network as much as possible. The expected benefit from this design principle is expected to be significantly lower network energy consumption, better scalability, higher degree of forward compatibility, lower interference from system overhead signals and consequently higher throughput in low load scenario, and also improved support for user centric beam-forming.
Advanced Antenna Systems (AAS) is an area where technology has advanced significantly in recent years and where we also foresee a rapid technology development in the years to come. Hence it is natural to assume that advanced antenna systems in general and massive Multiple Input Multiple Output (MIMO) transmission and reception in particular, will be a cornerstone in a future 5G wireless communication network.
As beam-forming becomes increasingly popular and capable it becomes natural to use it not only for transmission of data but also for transmission of control information. This is one motivation behind the relatively new control channel in LTE known as enhanced Physical Downlink Control CHannel (ePDCCH). When a control channel is beam-formed, the cost of transmitting the overhead control information can be reduced due to the increased link budget provided by additional antenna gain. This is a good property that likely will be utilized also for 5G, perhaps to an even larger degree than what is possible in the currently in LTE.
Despite advanced radio network planning tools, it is very difficult to predict the radio propagation in detail. As a consequence, it is difficult to predict which base stations that needs to have a relation and perhaps also a direct connection prior to the network deployment. This is addressed in LTE, where UEs can be requested to retrieve unique information from the system information broadcast of unknown base stations and report to the serving base station. Such information is used to convey messages to the unknown base station via the core network, which maintains a lookup table from a unique identifier to an established S1 connection. One such message is used to request transport network layer address information necessary for a direct base station to base station connection for the X2 interface.
The mobility procedure in 5G is planned to be beam based, where the reference signals defining such a beam is defined via specific Reference Signals (RS), that may be named Mobility Reference Signals (MRS), and can be activated by the node/s when a wireless communication device, such as a UE, is in need of making a handover. Thus the mobility procedure may be enabled via turning on a MRS on a selected set of beams, that may be named MRS beams, for the wireless communication device to measure and report back after which a network node decides on which such MRS beam will become the new serving beam for the wireless communication device in question. Which MRS beams to be transmitted by network nodes may depend on several factors including the current serving beam. Therefore, a network node may maintain a beam-to-beam relation table, that simply may be named a beam relation table, in order to refer which beam needs to be transmitted by the network node(s) to aid mobility of the wireless communication device.
In order for smooth operation of the mobility procedure in 5G, a 5G network node is need to have a concrete list of neighboring 5G nodes which can be handover candidates for wireless communication devices. In LTE, a corresponding neighbor relations table is established by using “always on signals” from the neighboring node(s). This is well studied for the Automatic Neighbor Relations (ANR) concept, see e.g. Evaluations of LTE Automatic Neighbor Relations”, Fredrik Gunnarsson et al, conference paper, Proceedings of the 73rd IEEE Vehicular Technology Conference, VTC Spring 2011, 15-18 May 2011, Budapest, Hungary.